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HOPCAT & Dark Galaxies

Discover findings from the HOPCAT project on dark galaxies, including HI detections, gravitational lensing, and optical galaxy matches. Explore the history, terminology, and characteristics of these mysterious astronomical entities.

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HOPCAT & Dark Galaxies

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  1. HOPCAT & Dark Galaxies Dr. Marianne T. Doyle Ph.D. Project University of Queensland

  2. Content Marianne Doyle Ph.D Project University of Queensland Advisor: Michael J. Drinkwater – UQ Assoc. Advisors: Elaine Sadler – Uni Sydney John Ross - UQ Collaborators David J. Rohde - UQ Kevin Pimbblet - UQ Mike Read – WFAU Edinburgh HIPASS Team – ATNF Parkes & Epping, Universities of : Melbourne, Cardiff, Western Sydney Macarthur, Wales, Swinburne, Technology Sydney, New Mexico, Manchester, Colorado, Sydney, Leicester ASTRON The Netherlands, AAO Sydney, WIYN Tucson etc…....... • Astronomy & I • The history of Dark Galaxies • HOPCAT & Isolated Dark Galaxies • Results BAS Meeting March 2007

  3. Astronomy & I • Always wanted to be an astronomy • Single parent & broke my leg in 1994 Wonderful kite! • High school 1995/6 - Complete senior subjects • Undergraduates degree: 1997 to 2001 • First Class Honours 2002 • July - Submitted my PhD Thesis yesterday (hung over!) • Now a Doctor of Astrophysics BAS Meeting March 2007

  4. http://www.hollywoodjesus.com/movie/disney/walt_mickey.jpg Disney (1979) BAS Meeting March 2007

  5. Mike Disney - Nature (1979 ) • “Strong indirect evidence already exists that our knowledge of galaxies is heavily biased by the sky background…” • Hitchhikers Guide to the galaxy & Cricket…….. • “No good reason for believing that low surface brightness (LSB) objects, and parts of objects, do not exist” • Extreme case of LSB galaxies are dark galaxies BAS Meeting March 2007

  6. Credit J. Bahcall (IAS, Princeton), M. Disney (Univ. Wales), NASA Dark Galaxies? • Term first used by astrophysicist investigating Quasars using gravitational lensing - (Mike Hawkins 1997) • Quasars (QUASi-stellAR objects) • Enormous energetic objects discovered in 1963 & lie near the edge of the observable universe • Gravitational lensing • Gravity can bend light • Gravity of massive foreground object lens the light of distant objects • In this case the massive foreground object was invisible BAS Meeting March 2007

  7. Is that a Dark Galaxy? • HIPASSJ1712-64 (Kilborn et al. 2000) • Extragalactic HI cloud with no Optical counterpart – high velocity cloud (HVC) • Dark galaxy DDO154? (Kennicutt et al. 2001) • An average, low-mass, dwarf irregular galaxy • HIPASSJ0731-69 (Ryder et al. 2001) • Tidal encounter with a moderately massive companion or ram-pressure stripping BAS Meeting March 2007

  8. Credits: UQ Communications and & Arna Karic, Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA, 94550, U.S.A UGC 10214 The Antennae Galaxies with their tidal tails. Courtesy of the NASA Astronomy Picture of the day web site (http://antwrp.gsfc.nasa.gov/apod/ap971022.html) BAS Meeting March 2007

  9. http://www.hero.ac.uk/uk/research/archives/2005/galactic_ghost.cfmhttp://www.hero.ac.uk/uk/research/archives/2005/galactic_ghost.cfm CREDIT: Arecibo Observatory / Cardiff University / Isaac Newton Telescope / Westerbork Synthesis Radio Telescope. CREDIT: Arecibo Observatory / Cardiff University / Westerbork Synthesis Radio Telescope. Or is this a Dark Galaxy? • VIRGOHI21 in the Virgo cluster • (Dr Robert Minchin, Mike Disney & Co 2005 – Cardiff University) • Australian Group dispute this is a dark galaxy • Tidal tail from NGC4254 BAS Meeting March 2007

  10. So what are Dark Galaxies? • Dark Galaxies: • Contain neutral hydrogen (fuel for star formation) • Possibly contain dark matter • Have no visible optical galaxy at the same position • No stars have formed • Gravitationally bound • Dark Galaxies are not: • Isolated HI clouds without structure • Very faint LSB galaxies • Tidal outflows from galaxies BAS Meeting March 2007

  11. Lets go looking for Isolated Dark Galaxies • How do we look? (since they are dark) • Neutral Hydrogen (HI) detections • Match the HI detections with optical galaxies • Investigate those with NO optical galaxies BAS Meeting March 2007

  12. http://www.cmis.csiro.au/features/NorthernSydney.htm Parkes Survey & Catalogue • HI Parkes All Sky Survey & catalogue HIPASS & HICAT • Largest blind HI radio survey of the southern sky • 4315 HI radio detected objects BAS Meeting March 2007

  13. HIPASS position uncertainty Optical Galaxy Match Objective: Find the optical galaxy for the HI radio sources Problem: Um….. Which galaxy was the original HI detection? Need an interactive program to visually match radio sources to their optical galaxy BAS Meeting March 2007

  14. 6 optical galaxy choice Original HICAT parameters Image Centred on HICAT positions Image Analysis ellipses Yellow for correct match Independent velocities Visually matched by 3 people to minimise galaxy selection bias BAS Meeting March 2007

  15. Results Optical counterparts for 84% of HICAT radio sources • Optically Matched with velocity 58% 2512 • Single Match (42% - 1798) • Compact group member (16% - 714) • Optically Matched with no velocity 26% 1106 • Single Match (20% - 848) • Compact group member (6% - 258) • No Guess 11% 481 • Several galaxies no velocities • Blank Field 5%216 • No visible galaxy BAS Meeting March 2007

  16. HOPCAT- Isolated Dark Galaxies? • 4315 HI radio detected objects • Dust extinction cut 3692 objects • Use only blank fields 13 objects BAS Meeting March 2007

  17. HOPCAT - Isolated Dark Galaxies? • Take out over crowded fields 2 objects • 2 remaining objects? • 1 - very faint previously observed optical galaxy in the Centaurus group – Banks et al (1999) • 1- non-detection - Narrow-band follow-up observations at Parkes (Thank you Dr. Ivy Wong) BAS Meeting March 2007

  18. HOPCAT - Isolated Dark Galaxies? No isolated dark galaxies are present within HOPCAT Doyle et al. (MNRAS 361,34–44, 2005) BAS Meeting March 2007

  19. http://milkyway.phys.tku.edu.tw/einmann/icons/Narrabri.gif Future? • No fame - Not finding any isolated dark galaxies is not as exciting as finding one (sigh!!!!) • Hopefully get to wear a floppy cap (i.e. be awarded a PhD and become Dr. Doyle. – I did graduate and I even bought the floopy cap! • Reduce data from observing runs at the Australia Telescope Compact Array and write another paper • Postdoctoral position somewhere - 2008 onwards BAS Meeting March 2007

  20. Inside the Eagle Nebula http://antwrp.gsfc.nasa.gov/apod/astropix BAS Meeting March 2007

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